Skellig Michael is one of only two World Heritage Sites in the Republic of Ireland and has undergone extensive conservation work in recent years under the authority of the Office of Public Works.

Michael Gibbons, a member of the Institute of Irish Archaeologists and a former co-ordinator of the OPW's Sites and Monuments Records Office, has criticised work on Skellig Michael several times, most recently in an article in History Ireland magazine where he claims that an altar used by pilgrims in the 1930s has been removed and that stonemasons are operating without supervision. Gibbons also claims that original features have been destroyed, that no conservation reports have been made public and "19th-century work practices persist".

The Sunday Tribune has seen a letter from senior architects working on the site, in which these claims are rebutted.

"Works being carried out on Skellig Michael are being carried out to the highest standard, " the letter from senior conservation architect Grellan D Rourke and senior archaeologists Dr Ann Lynch and Edward Bourke says.

"The current team involved in the work is highly skilled and multi-disciplinary."

The letter goes on to dispute several more claims from Gibbons involving curved lines of the site being replaced by sharp angles, and the absence of planning permission.

"Skellig Michael is a national monument in state ownership and the current work is part of an ongoing programme of conservation and consolidation which commenced in the early 1980s and which does not require planning permission, " they said.

Gibbons claims that "the potential value of Skellig Michael for future researchers is being destroyed" and that "genuine archaeological remains have been replaced by faux-monastic 21stcentury imitations". He also repeats claims made in a 2000 University College Cork MA thesis on heritage management at the Skelligs that the reconstruction of a monastic toilet at the site is "a work of fiction". A small oratory has been "virtually rebuilt", he says, while the layout of the site is "a work of imagination rather than being based on any surviving evidence".

Remarks first made by Gibbons on the Institute of Archaeologists of Ireland (IAI) website prompted the letter from those in charge of the Skellig Michael conservation. A spokesman for the OPW said it had dealt with the claims several times in the past.

The letter called on the IAI to "take responsibility for this material which is still on the website. . .

Mr Gibbons has been given a forum to make unsubstantiated and false remarks about the professional conduct of colleagues, at least some of whom are members of IAI, " the letter says.